A 65-year-old vegan man has macrocytic anemia with hypersegmented neutrophils, low vitamin B12, and loss of vibration sense in the lower limbs with extensor plantar responses. Folate replacement alone would correct his hematological parameters but fail to prevent progression of which complication?

• A Subacute combined degeneration of the spinal cord ✓
• B Megaloblastic change in bone marrow
• C Hypersegmentation of neutrophils
• D Elevated serum homocysteine

Explanation

Vitamin B12 is a cofactor for methylmalonyl-CoA mutase, and its deficiency causes demyelination of the dorsal and lateral columns producing subacute combined degeneration. Folate can remethylate homocysteine via methyltetrahydrofolate and thus correct the megaloblastic anemia, masking the B12 deficiency while the neurologic damage progresses. Homocysteine rises in both deficiencies, so it does not discriminate between them.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.